....CHDE......GB....LI..NL........................C0067481EUROPEAN PATENT APPLICATIONA219821222EP82200702.719820608enenen810281519810611NL19821222198251198212221982513 3B 65H 75/24 A 3B 65H 23/032 B 3B 65B 41/18 BdeAchse zum Festhalten einer Spule, Materialrolle oder dergleichenenShaft having means for retaining thereon a reel, material roll or similar articlefrArbre comportant des moyens pour retenir une bobine, rouleau de matériau ou article analogueTEVOPHARM SCHIEDAM B.V.00432510BO 30009 JWP.O. Box 35 Conradstraat 4NL-3100 AA SchiedamNLvan Maanen, Johannes DominicusBrahmstraat 6NL-2651 VK Berkel en RodenrijsNLvan der Beek, George Frans, Ir.et al00021481Nederlandsch Octrooibureau P.O. Box 297202502 LS 's-GravenhageNLCHDEGBLINL

An apparatus comprising a protruding shaft having means for retaining thereon a reel, material roll or similar article which is slipped on the shaft from the free end of the shaft, which means comprise a number of elongated pressure members located in recesses in the shaft. The pressure members are adapted to be displaced radially outwards by means of a pressurized fluid supplied through the shaft through a connector to be coupled with a source of pressurised fluid, until they engage against the inner side of the central cavity of a reel slipped on the shaft and to move radially inwards again for removing the reel from the shaft. The apparatus in particular serves for being applied in a packing machine in which articles are packed continuously in a packing material web unwound from a packing material roll retained on the shaft. Each pressure member is mounted in the associated recess also for a slideable movement in axial direction between a foremost and hindmost position and is provided at the end remote from the free end of the shaft with a stop projecting radially outwards for shifting the pressure members into the hindmost position by means of a reel slipped in the shaft and engaging the stops. Within the pressure members actuating means are mounted for an axially reciprocating movement, said actuating means being provided at their outer sides with at least one wedge surface cooperating with wedge surfaces formed at the inner sides of the pressure members so that by a movement of the actuating means from the one outmost position to the other outmost position the pressure members are urged radially outwards. Means are provided for returning of the pressure members into their foremost position again by a movement of the actuating means to the one outmost position, the actuating means having a stop surface bearing against a stop surface formed in the shaft in said outmost position of the actuating means. Means acting as a spring are provided urging the actuating means to said one outmost position. Further two spaces are defined in the shaft communicating with each other through a relatively narrow channel. A first valve member closes said channel in the one outmost position of the actuating means. The first space communicates directly with the connection to the source of a pressurized fluid so that in operation said space is filled with said pressurized fluid. The second space is bounded by a substantially transversely extending surface of the actuating means and is provided with a second normally closed valve member. The first valve member is coupled to the pressure member such that when said members are moved to a hindmost position the first valve member is opened, by which the pressurized fluid is permitted to flow into the second space through said channel so that the actuating mean is urged to the other outmost position by the fluid pressure acting on said transverse surface for displacing radially the pressure members by means of the wedge surfaces. By opening the second valve member the fluid pressure in the second space is relieved so that the actuating means are urged to the first outmost position again by the means acting as a spring.

Shaft having means for retaining thereon a reel, material roll or similar article.

The invention relates to an apparatus comprising a protruding shaft having means for retaiming thereon a reel,material roll or similar article which is slipped on the shaft from its free end, which means comprise a number of elongated pressure members located in recesses in the shaft, which by means of a pressurized fluid supplied through the shaft through a connection to be coupled with a source of pressurized fluid, can be displaced radially outwards until they engage the inner side of the central cavity of a reel slipped on the shaft and which can move radially inwards again for removing the reel from the shaft, which apparatus serves in particular for being applied in a packing machine in which articles are packed continuously in a packing material web unwound from a packing material roll retained on the shaft. Such an apparatus is known from the European Patent Application 79103930.8.

In the known apparatus under each pressure member an elongated bag of flexible material is provided, of which the inner side communicates with the connection to a source of a pressurized fluid and in which a no-return valve is positioned so that for the radial outwards displacement of the pressure members each bag associated with a pressure members has to be inflated by connecting the source of pressurized fluid to the connector during a predetermined time and for a radial inwards displacement of the pressure members the no-return valve has to be depressed in order to deflate the bags again. Moreover, the position of a reel retained on the shaft can vary within broad limits.

These are severe disadvantages of said apparatus, in particular in using it in a packing machine of the above mentioned type as in current high speed packing machines a finished packing material roll should also be rapidly exchangeable by a new roll, in particular in packing machines in which the end of the unwound material web is automatically spliced to the leading end of a second stand-by roll of packing material in the machine, and the depression of the no-return valve for shifting the finished roll from the shaft the coupling of the source of pressurized fluid after a new roll is slipped on the shaft consumes much time apart from the fact that said coupling may be forgotten easily by the operator, while by leakage the fluid pressure may decrease such that the roll is disengaged from the shaft. Besides, it is of greatest importance that the roll slipped and locked on the shaft is positioned accurately in a predetermined position as otherwise the packing machine cannot operate correctly.

The object of the invention is to provide an apparatus of the above mentioned type which does not have said disadvantages.

Said object is achieved in that in the apparatus according to the invention each pressure member is mounted also for a slideable movement in axial direction between a front and a rear position in the associated recess and is provided with a radially outwards protruding stop at the end remote from the free end of the shaft so that by means of a reel slipped on the shaft and in engagement with the stops, the pressure members can be shifted into the hind most position , while within the pressure members actuating means are mounted for an axially reciprocating movement, which at its outer side is provided with at least one wedge surface cooperating with wedge surfaces formed at the inner side of the pressing means so that by a movement of the actuating means from the one outmost position to the other the pressure members are urged radially outwards to their hind most position, and means are provided for returning the pressure members to the foremost position by a movement of the actuating means to the one outmost position, the actuating means having a stop surface bearing against a stop surface formed in the shaft in said one outmost position of the actuating means, and means acting as a spring are provided for urging the actuating means to said one outmost po= sition, and further two spaces in the shaft are defined communicating with each other through a relatively narrow channel, a first valve member being provided closing this channel in the one outmost position of the actuating means and the first space is in direct qom- munication with the connection to a source of pressurized fluid 5o that in the operative condition said space is filled with the pressurized fluid, and the second space is bounded by a substantially transversely extending surface of the actuating means and is provided with a second normally closed valve member, while the first valve member is connected to the pressing means such that in sliding said neans to their hind most position, the first valve member is opened by which the pressurized fluid is permitted to flow through said channel into the second space so that the actuating means is driven to the other outmost position by the fluid pressure acting on said transverse surface for the radial displacement of the pressure members by means of the wedge surfaces and by opening the second valve member the fluid pressure in the second space is relieved so that the actuating means is urged to the one outmost position again by said means acting as a spring.

In an apparatus constructed in this way a reel can be retained quickly in the correct position on the shaft by simply slipping the reel while in engagement with the stops to an end position on the shaft which end position is defined by the hind most rear position of the pressure members, said members being automatically displaced radially outwards for locking the reel. Moreover, the connection to the source of the pressurized fluid is maintained, by which any leakage is compensated for and the fluid pressure remains sufficiently high for retaining the reel on the shaft.

Preferable the means acting as a spring are formed by the fluid pressure in the first space, said space being bounded by a transverse surface of the actuating means which has a smaller area than the transverse surface of the actuating means bounding the second space and which faces in opposite direction.

Advantageously, at least the front portion of the shaft is hollow and the actuating means is formed by a sleeve disposed within this cavity and mounted for an axially slideable movement around a coaxial stub axle protruding into the cavity and connected to the shaft, said first space being enclosed by the front portion of the sleeve extending beyond the stub axle, which portion is substantially closed at the front side and communicates at the rear side with the connection for the coupling with a source of a pressurized fluid through a channel extending through the stub axle, while said second space is formed by the front portion of the cavity of the shaft between the closed front end of the sleeve and the closed front end of the hollow shaft.

The channel connecting the first and second space to each other may extend through the front closure of the first space and the first valve member may be formed by a valve element engaging the front side of said front closure in the one outmost position of the actuating means so that thereby the outlet of the channel into the second space is closed and said element in the other outmost position of the actuating means is spaced apart therefrom.

Preferably the valve element is provided on the front end of a rod extending through a aperture in the front closure so that said closure is permitted to slide along the rod, in a spring seat being fixed on the rod near its rear end for supporting a spring at its one side, which at its other side engages the front closure, while the spring seat in a movement of the actuating means to the other outmost position engages the front end of the stub axle, and the actuating means has a stop surface engageable by the stops formed on the pressure members, such that in a sliding movement of the pressure members to the hind-most position the actuating means is carried along and in a movement of the actuating means to the one outmost position the pressure members are shifted in the foremost position again.

The pressure members may be retained in the recesses in the shaft by means of tension springs extending through apertures in said shaft.

As already mentioned above in the apparatus according to the invention it is assured that a material roll of a certain width is locked on the shaft in a correct position with respect to the packing machine. However, it is frequently desired in a packing machine, that packing materials of different widths can be used, which means that preferably the position of a material roll on the shaft with respect to the packing machine should be variable. According to the invention this is achieved in that the shaft is supported for an axially sliding movement and means are provided for reciprocating the shaft.

In this way, by an axially sliding movement of the shaft the position in which a material roll is locked on the shaft, which position is defined by the hind most position of the pressure members can be varied transversely with respect to the packing machine so that packing material rolls of different widths can be used in one and the same packing machine. In manufacturing a packing material roll during spooling the material into a roll, or by drying of the Jacking material, differences in strain may occur between the side adges of the material web, by which in unwinding, the material web is curved slightly which can lead to detracking of the material web in the packing machine. Therefore, it is desired in the operation of the packing machine to be able to regulate the material web extending from the packing material roll to the packing machine in the transverse direction in order to prevent detracking of the material web.

Advantageously, therefore the slidability of the shaft according to the invention is utilized, the means for shifting the shaft comprising a motor controlled by signal means which in the event of a deviating transverse position of at least one side edge of the packing material web produces a signal for actuating the motor, by which the shaft is displaced in a predetermined direction to correct the position of the side edge.

Preferably a timing device is provided which after the actuation of the motor by said signal stops again the motor after a displacement of the shaft over a predetermined distance is obtained, and a controlling device by which after stopping the motor and after a predetermined length of the material web having passed said device a signal from the signal means is passed again to the motor.

In this way it is achieved that the shaft is axially shifted stepwise and always after such a step it is determined by the signl means whether by shifting the shaft the deviating position of the packing material web sensed by said means is corrected sufficiently by which it is prevented that the shaft is shifted too far for correcting the position of the material web, so that the shaft should be shifted in opposite direction again resulting in the material web being not in the correct position during a relatively long time.

Advantageously the signal means are formed by two photocells spaced apart transversely of the material web and arranged near an edge of the material web such that in a correct position of said edge the one photocell is facing the material web at a relative short distance from said edge and that the other photocell is at a relatively short distance from the edge outside of the material web.

In this way, in a correct position of the material web only said one photocell delivers a signal and in a faulty position of the material either both of the photocells deliver a signal or of the photocells do not deliver a signal.

The controlling device is preferably formed by a photocell disposed at a predetermined position between the signal means and the shaft and adapted to deliver a signal when a mark provided on the packing material web passes said photocell and by a counting device capable of counting a predetermined number of said signals.

In a packing machine it can happen that for example by dirt entering the guidings of the articles to be packed the packing material web deviates so much from the correct position that for correcting said deviating position the shaft should be shifted in one direction over a large distance which is undesirable.

Therefore, preferably a protruding plate is connected to the shaft journalled for a sliding movement, which plate has a predetermined width parallel to the axis of the shaft, while a substantially fixedly arranged inductive sensor is provided which is directed approximately to the center of said plate, and capable of delivering a signal when an edge of the plate, passes said sensor by which the packing machine is stopped.

It is noted that from the European Patent Application 80301268.1 a guiding system for a material web is known, in which said web is passed over two rollers mounted for a movement so that their axis are tilted, while said rollers are controlled by signal means sensing the edges of the material web by means of infrared radiation.

The invention will be explained in detail with reference to the drawings, in which:

As shown in Fig.1 the apparatus according to the invention comprises a shaft 1 and a hollow shaft 2 surrounding it and closed by the nose piece 3 at the front side. The shaft 1 comprises a stub axle 4 located within the hollow shaft 2 and having a front portion 4a along which the sleeve-shaped actuating means 5 is permitted to slide in axial direction. In the hollow shaft 2 a number of recesses 6 is provided in which the pressure members 7 are positioned which are retained in the recesses 6 by tension springs 8 extending through apertures in the pressure members 6.

From the figure appears that the recesses 6 have a slightly larger length than the pressure members 7 so that the latter are permitted to slide in axial direction between a foremost position shown in the lower part of the figure and a hindmost position shown in the upper part of the figure. Each pressure members 7 has a stop 9 extending radially outwards against which the reel or material roll 10 slipped on the shaft can bear.

Further the pressure members 7 are provided with two sets of wedge surfaces 11 and 12 cooperating with wedge surfaces formed at the external side of the actuating means 5 so that in sliding of the actuating means 5 from the one outmost position indicated in the lower part of the figure to the other outmost position indicated in the upper part of the figure, the pressing means 7 are displaced radially outwards.

Moreover the pressure members 7 are provided with stop surface 13 cooperating with the stop surface 14 of the actuating means 5. The front portion of the actuating means 5 extends beyond the end of the stub axle portion 4a so that a space 15 is defined communicating with the connection 17 with a source of pressurized fluid shown in Fig. 2, by means of the channel 16 extending through the shaft 1 and the stub axle 4, 4a.

The space 15 is closed at the front end by the front closure 18 through which a relatively narrow channel 19 extends. Through the front closure 18 a slideable stem 20 extends carrying at its front end the valve element 21 and at its rear end a spring seat 22, retained by a screwed on nut. Between said spring seat 22 and front closure 18 a spring 23 is located. In the nose piece 3 a second space 24 is defined and in the nose piece a valve 25 is provided adapted to be forced open by means of the press-button 26. Further in the nose piece 3 a stop surface 27 is formed against which the front end of the actuating means 5 bears in said one outmost position of said means.

In the lower half of Fig. 1 the situation is shown, in which no reel 10 is provided on the shaft or in which the reel 10 is slipped on the shaft but is not yet in engagement with the stops 9. In the space 23 a constant pressure of the pressurized fluid supplied by the channel 16 is operative by which as result of the fluid pressure exerted on the rear end of the front closure 18, the actuating means 5 is pushed against the stop member 27.

Thereby, the valve element 21 is pushed against the front side of the front closure 18 by the spring 23 so that the end of the channel 19 opening into the second space 24 is closed.

Now, when the reel 10 is slipped further on the shaft said reel engages the stops 9 so that in pushing the reel 10 still further on the shaft the pressure members 7 are shifted in the hindmost position is shown in the upper part of the figure. By means of the stop surfaces 13, 14 the actuating means 5 is carried along, by which the front closure 18 is shifted rearwards along the stem 20 in which the spring seat 22 abuts the front end of the front portion 4a of the stub axle and the channel 19 is released from the valve element 21. The pressurized fluid in the space 15 is now permitted to flow through the channel 19 into the second space 24, by which a pressure is exerted on the front side of the front closure 18 and the actuating means 5 is shifted further to the right into the other utmost position indicated in the upper part of the figure so that by means of the wedge surfaces 11, 12 the pressure members 7 are displaced radially outwards and engage the inner side of the center space in the reel 10, by which said reel 10 is locked and indeed in a predetermined position defined by the hindmost position of said pressure members 7.

For shifting a reel In from the shaft the press-button 26 is depressed, by which the pressure in the space 24 is released so that no pressure is exerted on the front end of the front closure 18 and the actuating mean 5 is urged to the left into the one outmost position by the fluid pressure in the space 15, and the channel 19 is closed by the valve element 21. Thereby, and pressure members 7 are first moved radially inwards by the tension spring 8 and thereafter shifted again into their foremost position because the stop surface L7 engages the surface 13.

As shown in Fig.2 the shaft 1 is supported for a free rotation and sliding movement in the bearings 28 and 29 mounted in the frame 30. With 31 a brake drum provided on the shaft 1 is indicated and with 32 a brake shoe. A sleeve 33 is mounted on the shaft 1, through the ball bearing 34 said sleeve 33 being provided with teeth 35 are in meshing engagement with the teeth of the gear 36. The gear 36 can be driven in rotation in both directions by means of the motor 37 and a reduction mechanism in the box 38.

To the sleeve 33, by means of the screw 39 a plate-shaped member 40 is fixed to which is facing an inductive sensor 41.

As shown in Fig. 3 a packing machine comprises two shafts 2, 2' shown in Fig. 1 and 2 on which the material web rolls 10 and 10' are retained. In packing the articles 42 a material web 43 is unwound from the on roll 10 , whereas the packing material roll 10' is in the stand-by condition so that by means not shown the trailing end of the material web 43 unwound from the roll 10 is automatically spliced to the leading end of the material web 10' so that the packing machine can operate continuously when the material roll 10 is depleted. Then, the finished roll 10 can be exchanged by slipping a new roll on the shaft 2, so that said roll will be in the correct position automatically. This position substantially defined by the hindmost position of the pressure members 7 is preadjusted by shifting the shaft 1. If after packing a number of articles 42, other articles have to be packed in the packing machine, in which a packing material of a different width has to be used, then the shafts 2 and 2' are shifted into the correct position so that each packing material roll locked on said shafts are in the correct position again with respect to the packing machine.

As shown in the figures 3 and 4 there are two photocells 44 and 45 are arranged above the material web near one of their side edges. The photocell 44 is directed at said web at a short distance from the side edge of the material web and the photocell 45 is directed at a point located outside the material web 44 at a short distance from said edge so that in the correct position of said edge shown in Fig. 4, only by the photocell 44 a signal is excited, in which correct position the material web 43 is guided correctly in the folding box 46 of the packing machine so that also the articles 42 are packed correctly. However, if by some reason the edge of the material web 43 is shifted to a lower position with respect to the position shown in Fig. 4 so that also the photocell 4 is directed at a point outside said material web, then a signal is delivered to the motor 37 by which the motor is activated during a short time through a time relay not shown so that the shaft 1 is shifted through the gear 36 over a predetermined distance in the direction opposite to the direction in which the edge of the material web has been displaced. From said moment, by means of a pulse counter (not shown) a predetermined number of pulses is counted, said pulses being produced in that marks on the material web 43 pass the photocell 47. This number is defined such that the number of counted pulses at least equals the number of marks on the portion of the material web 43 between the photocells 44, 45 and the shaft 1, so that when said number is reached the effect of the displacement of the shaft 1 has reached the photocells 44 and 45. If by the displacement of the shaft 1, the edge of the material web has not come in the correct position yet, then by the signal from the photocells 44, 45 the motor 37 is activated again during a certain time. Said steps are repeated if necessary until the edge of the material web is in the correct position.

The above mentioned steps are also carried out when the edge of the material web 43 is shifted to a higher position with respect to the position shown in Fig. 4 so that also by the photocell 45 a signal is delivered.

In the event of an extensive deviation from the correct position of the edge of the material web, for example as result of dirt entering the folding mechanism in the folding box 46, the shaft 1 is shifted in one direction over such a great distance that the inductive sensor 41 is directed at a point outside one of the side edges of the plate-shaped member 40, by which the packing machine is switched off.

In Fig. 3 the compensation arms 48 and 48' are still shown each connected to the brake shoe 32 associated with the respective shaft 1.

 1. Apparatus comprising a protruding shaft having means for retaining thereon a reel, material roll or similar article which is slipped on the shaft from the free end of the shaft, which means comprise a number of elongated pressure members located in recesses in the shaft adapted to be displaced radially outwards by means of a pressurized fluid supplied through the shaft through a connector to be coupled with a source of pressurized fluid, until they engage against the inner side of the central cavity of a reel slipped on the shaft and to move radially inwards again for removing the reel from the shaft, which apparatus in particular serves for being applied in a packing machine in which articles are packed continuously in a packing material web unwound from a packing material roll retained on the shaft, characterized in that each pressure member is mounted in the associated recess also for a slideable movement in axial direction between a foremost and hindmost position and is provided at the end remote from the free end of the shaft with a stop projecting radially outwards for shifting the pressure members into the hindmost position by means of a reel slipped on the shaft and engaging the stops, while within the pressure members actuating means are mounted for an axially reciprocating movement, said actuating means being provided at their outer sides with at least one wedge surface cooperating with wedge surfaces formed at the inner sides of the pressure members so that by a movement of the actuating means from the one outmost position to the other outmost position the pressure members are urged radially outwards, and means are provided for re- turning of the pressure members into their foremost position again by a movement of the actuating means to the one outmost position, the actuating means having a stop surface bearing against a stop surface formed in the shaft in said one outmost position of the actuating means, and means acting as a spring are provided urging the actuating means to said one outmost position, and further two spaces are defined in the shaft communicating with each other through a relatively narrow channel, a first valve member being provided closing said channel in the one outmost position of the actuating means and the first space communicating directly with the connection to the source of a pressurized fluid so that in operation said space is filled with said pressurized fluid, and the second space is bounded by a substantially transversely extending surface of the actuating means and is provided with a second normally closed valve member, while the first valve member is coupled to the pressure member such that when said members are moved to a hindmost position the first valve member is opened, by which the pressurized fluid is permitted to flow into the second space through said channel so that the actuating mean is urged to the other outmost position by the fluid pressure acting on said transverse surface for displacing radially the pressure members by means of the wedge surfaces, and by opening the second valve member the fluid pressure in the second space is relieved so that the actuating means are urged to the first outmost position again by the means acting as a spring. 2. Apparatus according to claim 1, characterized in that the means acting as a spring are formed by the fluid pressure in the first space, said space being hounded by a transversely extending surface of the actuating means which has a smaller area than the transverse surface of the actuating means bounding the second space and which is faced in an opposite direction. 3. Apparatus according to claim 2, characterized in that at least the front portion of the shaft is hollow and the actuating means is formed by a sleeve disposed within said cavity and mounted for an axially slideable movement around a stub axle connected to the shaft and extending coaxially in the cavity, said first space being enclosed by the front part of the sleeve extending beyond the stub axle which portion is closed substantially at the front side and at the rear side communicates with the connection for the coupling with a source of a pressurized fluid through a channel extending through the stub axle, and said second space is formed by the front portion of the cavity of the shaft between the closed front end of the sleeve and the closed end of the hollow shaft. 4. Apparatus according to claim 3, characterized in that the channel connecting the first and second space with each other extends through the front closure of the first space and the first valve member is formed by a valve element which in the one outmost position of the actuating means engages the front side of said front closure so that thereby the outlet of the channel in the second space is closed and which in the other outmost position of the actuating means is spaced apart therefrom. 5. Apparatus according to claim 4, characterized in that a valve element is provided on the front end of a rod extending through an aperture in the front closure so that said closure is permitted to slide along the rod, a spring seat is being fixed on the rod near its rear end for supporting at one side a spring engaging with its other end the front closure while the spring seat in a movement of the actuating mean to the other outmost position engages the front end of the stub axle, and the actuating means has an stop surface engageable by the stops formed on the pressure members, such that at shifting the pressure members to the hindmost position the actuating means is carried along and in a movement of the actuating means to the one outmost position the pressure members are shifted to their foremost positions again. 6. Apparatus according to claims 1-5 characterized in that the pressure members are retained in the recesses in the shaft by means of tension springs extending through apertures in said means. 7. Apparatus according to claims 1-6, characterized in that the shaft is supported for an axially sliding movement and means are provided for reciprocating the shaft. 8. Apparatus according to claim 7, characterized in that the means for shifting the shaft comprise a motor controlled by signal means adapted to deliver a signal for activating the motor in the event of a deviating transverse position of at least one side edge of the packing material web by which the shaft is displaced in a predetermined direction to correct the position of the side edge. 9. Apparatus according to claim 8, characterized in that a timing device is provided which after the activation of the motor by said signal stops again said motor after a displacement of the shaft over a predetermined distance is reached, and a controlling device is provided by which after stopping the motor and after a predetermined length of the material web has passed said device, a signal from the signal means can be transmitted again to the motor. 10. Apparatus according to claim 8 or 9, characterized in that the signal means are formed by two photocells spaced apart in the transverse direction with respect to the material web and ar ranged near an edge of the material web such that in a correct position of said edge the one photocell is directed on the material web at a relatively short distance from said edge and the other is located outside the material web at a relatively short distance from said edge. 11. Apparatus according to claim 9 orl0, characterized in that the controlling device is formed by a photocell located in a predetermined position between the signal means and the shaft and adapted to deliver a signal when a mark provided on the packing material web passes said photocell by a mark provided on the packing material web, and a counting device capable of counting a predeetermined number of said signals. 12. Apparatus according to claims 7-11, characterized in that a protruding plate is connected to the shaft journaled for a sliding movement, which plate has a defined width extending parallel to the axis of the shaft, whilE a substantially fixedly arranged inductive sensor is provided whict is directed approximately to the center of said plate, said sensor being capable of delivering a signal when an edge of the plate passes said sensor, by which the packing machine is stopped.